This invention relates to apparatus for transporting magnetic particles, and more particularly to improvements in apparatus for transporting finely divided dry magnetic ink particles and presenting the same in a uniform layer for transfer to suitable receptor means.
In the art of non-impact printing using dry magnetic ink, it is a known practice to transfer magnetic ink characters to a paper web by passing the web between an ink source and selectively energizable electrostatic print heads. It is also a known practice to form a latent magnetic image on the magnetizable surface of a drum as the receptor means, and to a develop the latent image by deposition thereon of finely divided particles of magnetic ink, which adhere only to the magnetized image areas. The adherent ink is then transferred from the drum to a paper web, or the like, and the ink image is made permanent by a suitable fixing process.
For any of the foregoing or other known similar systems, printing quality is a function of the degree of uniformity of ink transfer, and to this end resort has been had to belts for transporting the ink in a uniform layer for transfer to the receptor means.
In one known, preferred apparatus, a non-translating, rotating dry magnetic ink bead is formed, by suitably positioned magnet means, along a transverse surface portion of a transport belt, and the rotating ink bead operates uniformly to distribute the magnetic ink over the surface of the belt for subsequent transfer to the receptor means.
Difficulties have been encountered, however, in apparatus of this type, since the bead-forming magnet means must include flux forming elements disposed to the side of the belt opposite the ink, so that the magnetic flux extends through the surface of the belt with sufficient strength and concentration to form a well defined bead of ink. A thin, flexible belt of a material such as nickel meets this requirement, but due to its inherent lack of rigidity has been found difficult to guide and support in order to maintain suitable dimensional tolerances. Known belt guiding and supporting means achieving these tolerances have been found to introduce cyclic strains in the belt, leading to untimely belt failure.
It is a general objective of this invention to provide improved means for transporting magnetic particles for presentation in a uniform layer in a transfer region.
It is a further general objective of this invention to provide improved dry magnetic ink transporting apparatus capable of presenting a uniform layer of magnetic ink in a region of transfer thereof to suitable receptor means.
Another object of the invention is to provide improved means for forming and maintaining a non-translating, rotating dry magnetic ink bead on the surface of a rotatable ink transporting belt to form a uniform layer of ink thereon.
A still further and more specific objective of this invention is to provide improved means for supporting and guiding a thin, flexible, cylindrically configured rotatable dry magnetic ink transport belt in close proximity to magnet pole pieces disposed adjacent the belt to form a non-translating, rotating bead of ink thereon.